As indicated above, it is well known in the art that gear pumps are useful for mixing a gas into a liquid. In all such gear pump mixers, a motor drive must be provided to rotate the gears within the gear chamber.
Such coupling of a motor and a gear pump is a relatively heavy and complex combination. These factors are not overriding or even particularly important for most applications, but in some instances it is desirable to mix a gas and liquid directly adjacent to a dispersing nozzle. In this instance the weight and size of a motor driven pump can be a disadvantage and a limitation, as for example where the mixer is to be located right at the nozzle or dispensing apparatus through which a hot melt adhesive foam is to be dispensed. The problem is especially acute if a mixer is to be provided in a hand held gun, because of the size and weight of the motor driven pump mixer. The problem again arises where a gas/liquid mixture is to be delivered from a mixer through a long hose to a nozzle, from which it is dispensed discontinuously with intermittent periods of inaction, for example overnight. During such quiescent periods the mixture in the hose may tend to separate and, when later dispensed, the separated gas may cause "spitting" or nonuniform delivery from the gun. Where this is a concern, the problem could of course be overcome by the provision of a return line, but that would require another length of heated hose.
In other instances, where the gas reacts with the liquid after mixing, it may be desirable to bring them together just upstream of the dispensing nozzle, so that the reaction cannot progress to an undesirable extent during the short period of travel to the nozzle.
As yet another example, where mixtures of different gases and liquids, or mixtures of different gas/liquid ratios, are to be supplied to separate nozzles, it is necessary to provide separate mixers (either adjacent a supply, or adjacent each nozzle) for accomplishing the separate mixings. The motor driven pumps previously available may be undesirably expensive for some applications.
Against this background, it has been the primary objective of this invention to provide mixing means which are relatively lightweight, simple and less expensive, in comparison to gear motor-pump mixers, and which can be used adjacent a dispenser nozzle.